When peripheral equipment is added to a personal computer or a notebook personal computer taking into account space saving, there are an increasing number of cases where devices conforming to a USB, which is a general-purpose standard, are used. In particular, from the viewpoint of portability of data, the use of a removable drive (a detachable external storage medium) conforming to the USB has been spread. This tendency is not limited to the personal computer. In recent years, the degree of the spread is increasing in industrial equipments such as a programmable display device, which is a touch panel type display and operation apparatus.
Usually, a removable drive device connected to an electronic apparatus such as a personal computer is managed by the connection target electronic apparatus after a drive number is allocated to the removable drive device. For example, when a removable drive device is mounted on an apparatus such as a personal computer, which is a connection target of the removable drive device, in general, the drive number to be allocated to the removable drive device is set in order from the lowest one among unused drive numbers (actually, the drive numbers are often alphabets such as A, B, and C rather than numerical values). In a general-purpose operating system of a personal computer, the drive number of a previously mounted removable drive can be reallocated. The removable drive once allocated with a drive number realizes a function in which the drive number designated last time is automatically allocated even when the removable drive is removed and attached again.
Concerning allocation of a drive number, there is proposed a method of giving information for specifying a drive number to an external storage medium (hereinafter referred to as a removable device) itself such as a memory card or a USB memory mounted on a removable drive device to fix a drive number allocated to the mounted removable device (Patent Literature 1).
There is proposed a method of allocating a corresponding drive number to each of connection ports (interfaces) of a built-in device to fix a drive number of a removable drive connected to the connection port (Patent Literature 2).